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Atmospheric Circulation and Weather Systems

Atmospheric Circulation and Weather Systems

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Study Action Plan (Sorted by Difficulty)
Air Masses and Fronts
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Atmospheric Pressure and Wind Systems
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ENSO and its Global Impact
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Extra Tropical and Tropical Cyclones
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Forces Affecting Wind Velocity and Direction
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General Atmospheric Circulation
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Local Wind Systems
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Vertical and Horizontal Pressure Variations
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Learning Objectives

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Learning Objectives

  • Understand the causes of atmospheric pressure differences and their role in atmospheric circulation and weather disturbances, including tropical storms.
  • Examine vertical and horizontal variations in atmospheric pressure and their influence on wind direction and velocity.
  • Analyze the effects of pressure gradient force, frictional force, and Coriolis force on wind velocity and direction, including the formation of geostrophic winds and cyclonic circulations.
  • Describe the global wind patterns driven by latitudinal heating variations, pressure belts, and Earth's rotation, including Hadley, Ferrel, and Polar cells.
  • Explore the formation and classification of air masses and the dynamics of fronts, including cold, warm, stationary, and occluded fronts.
  • Differentiate between extra tropical and tropical cyclones, their formation, structure, and impact, including the role of fronts and the Coriolis effect.
  • Explain local wind phenomena such as land and sea breezes, mountain and valley winds, and their impact on regional climates.
  • Discuss the El Nino-Southern Oscillation (ENSO) phenomenon, its causes, and its significant impact on global weather patterns and climate variability.

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Revision Notes & Summary

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Chapter Notes

Atmospheric Pressure and Wind Systems

  • Atmospheric Pressure: The weight of a column of air from the mean sea level to the top of the atmosphere, expressed in millibars (mb). At sea level, the average atmospheric pressure is 1,013.2 mb.
  • Wind: Air in horizontal motion, moving from high pressure to low pressure areas.
  • Weather Disturbances: Formed by the interaction of different air masses, leading to phenomena like tropical storms.

Vertical and Horizontal Pressure Variations

  • Vertical Pressure Variation: Pressure decreases rapidly with height, approximately 1 mb per 10 m increase in elevation.
  • Horizontal Pressure Variation: Studied using isobars, lines connecting places of equal pressure. Pressure systems include low-pressure (cyclones) and high-pressure (anticyclones) systems.

Forces Affecting Wind Velocity and Direction

  • Pressure Gradient Force: Causes wind to blow from high to low pressure areas.
  • Frictional Force: Affects wind speed, greatest at the surface.
  • Coriolis Force: Deflects wind due to Earth's rotation, to the right in the northern hemisphere and to the left in the southern hemisphere.
  • Geostrophic Wind: Wind that blows parallel to isobars when pressure gradient force is balanced by Coriolis force.

General Atmospheric Circulation

  • Global Wind Patterns: Driven by latitudinal heating variations, pressure belts, and Earth's rotation.
  • Cells: Hadley, Ferrel, and Polar cells describe the circulation patterns in different latitudes.

Air Masses and Fronts

  • Air Masses: Large bodies of air with uniform temperature and humidity, classified by their source regions (e.g., maritime tropical, continental polar).
  • Fronts: Boundaries between different air masses, including cold, warm, stationary, and occluded fronts.

Extra Tropical and Tropical Cyclones

  • Extra Tropical Cyclones: Develop in mid and high latitudes, characterized by a clear frontal system.
  • Tropical Cyclones: Originate over warm tropical oceans, characterized by strong winds and heavy rainfall. Known as cyclones, hurricanes, typhoons, or willy-willies depending on the region.

Local Wind Systems

  • Land and Sea Breezes: Caused by differential heating of land and sea, leading to sea breezes during the day and land breezes at night.
  • Mountain and Valley Winds: Daytime upslope winds (valley breeze) and nighttime downslope winds (mountain breeze).

ENSO and its Global Impact

  • ENSO (El Nino-Southern Oscillation): A climatic phenomenon involving the warming of central Pacific Ocean waters, affecting global weather patterns, such as causing heavy rainfall in South America and droughts in Australia and India.
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Practice Test – MCQs, True/False

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Multiple Choice Questions

A.

The absence of the Coriolis force at the equator.

B.

The presence of high pressure systems at the equator.

C.

The lack of sufficient sea surface temperature near the equator.

D.

The presence of strong vertical wind shear at the equator.
Correct Answer: A

Solution:

Tropical cyclones require the Coriolis force to develop their characteristic rotation, which is absent at the equator, preventing cyclone formation.

Chapter Concept:

General Atmospheric Circulation

A.

Increased rainfall on the arid west coast of South America

B.

Droughts in the Amazon rainforest

C.

Enhanced monsoon activity in India

D.

Decreased hurricane activity in the Atlantic Ocean
Correct Answer: A

Solution:

During a strong ENSO event, the warm waters of the central Pacific Ocean drift towards the South American coast, causing increased rainfall in typically arid regions.

Chapter Concept:

ENSO and its Global Impact

A.

Clockwise

B.

Counterclockwise

C.

Parallel to isobars

D.

Perpendicular to isobars
Correct Answer: A

Solution:

In the Northern Hemisphere, wind circulates clockwise around a high-pressure system.

Chapter Concept:

Forces Affecting Wind Velocity and Direction

A.

It involves air rising at the equator and sinking at 30° N and S.

B.

It involves air sinking at the equator and rising at the poles.

C.

It involves air moving directly from the poles to the equator.

D.

It involves air moving from the equator to the poles without sinking.
Correct Answer: A

Solution:

The Hadley cell is characterized by air rising at the equator due to convection and sinking at around 30° N and S, forming a circulation pattern.

Chapter Concept:

General Atmospheric Circulation

A.

1,013.2 mb

B.

1,000 mb

C.

1,100 mb

D.

900 mb
Correct Answer: A

Solution:

The average atmospheric pressure at sea level is 1,013.2 millibars.

Chapter Concept:

Atmospheric Pressure and Wind Systems

A.

It decreases wind velocity

B.

It has no effect on wind velocity

C.

It increases wind velocity

D.

It reverses wind direction
Correct Answer: C

Solution:

The pressure gradient force increases wind velocity as it is stronger where isobars are closer.

Chapter Concept:

Forces Affecting Wind Velocity and Direction

A.

It deflects the wind to the left.

B.

It deflects the wind to the right.

C.

It has no effect on wind direction.

D.

It causes wind to blow parallel to isobars.
Correct Answer: B

Solution:

In the Northern Hemisphere, the Coriolis force deflects the wind to the right.

Chapter Concept:

Vertical and Horizontal Pressure Variations

A.

Pressure Gradient Force and Frictional Force

B.

Coriolis Force and Gravitational Force

C.

Pressure Gradient Force and Coriolis Force

D.

Gravitational Force and Frictional Force
Correct Answer: C

Solution:

In geostrophic winds, the pressure gradient force is balanced by the Coriolis force, causing the wind to blow parallel to isobars.

Chapter Concept:

Forces Affecting Wind Velocity and Direction

A.

The Coriolis force would increase, causing greater deflection of wind paths.

B.

The pressure gradient force would decrease, leading to weaker wind speeds.

C.

The Hadley cell would expand, covering more latitudinal area.

D.

The subtropical high-pressure belts would shift towards the poles.
Correct Answer: A

Solution:

If the Earth's rotation speed increases, the Coriolis force, which is directly related to the rotation speed, would increase. This would cause a greater deflection of wind paths, affecting the general atmospheric circulation patterns.

Chapter Concept:

General Atmospheric Circulation

A.

The Coriolis force would increase, causing greater deflection of winds.

B.

The Coriolis force would decrease, leading to less deflection of winds.

C.

There would be no change in the Coriolis force.

D.

Winds would stop altogether.
Correct Answer: A

Solution:

Doubling Earth's rotation speed would increase the Coriolis force, resulting in greater deflection of winds from their original path.

Chapter Concept:

Vertical and Horizontal Pressure Variations

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True or False

Correct Answer: False

Solution:

In the northern hemisphere, the Coriolis force deflects wind to the right, not to the left.

Chapter Concept :

Atmospheric Pressure and Wind Systems

Correct Answer: True

Solution:

The Coriolis force is directly proportional to the angle of latitude, being zero at the equator and maximum at the poles.

Chapter Concept :

General Atmospheric Circulation

Correct Answer: False

Solution:

Horizontal pressure variations are significant in determining wind direction and velocity, as small differences in pressure can greatly influence these factors.

Chapter Concept :

Vertical and Horizontal Pressure Variations

Correct Answer: True

Solution:

An air mass is indeed defined as a large body of air with consistent temperature and moisture characteristics, acquired from its source region.

Chapter Concept :

Air Masses and Fronts

Correct Answer: False

Solution:

Tropical cyclones originate only over the sea and dissipate upon reaching land, whereas extra tropical cyclones can originate over both land and sea.

Chapter Concept :

Extra Tropical and Tropical Cyclones

Correct Answer: True

Solution:

Geostrophic winds result from the balance between the pressure gradient force and the Coriolis force, causing the wind to flow parallel to the isobars.

Chapter Concept :

Forces Affecting Wind Velocity and Direction

Correct Answer: False

Solution:

Land breezes occur at night when the land cools down faster than the sea, causing air to descend over the land and create a high-pressure area.

Chapter Concept :

Local Wind Systems

Correct Answer: False

Solution:

Mountain winds occur at night when the slopes cool down, causing dense air to descend into the valley.

Chapter Concept :

Local Wind Systems

Correct Answer: True

Solution:

ENSO is closely associated with pressure changes in the Central Pacific and Australia, leading to droughts in Australia during strong ENSO events.

Chapter Concept :

ENSO and its Global Impact

Correct Answer: True

Solution:

Extra tropical cyclones are characterized by a well-developed frontal system, whereas tropical cyclones do not have such a system.

Chapter Concept :

Extra Tropical and Tropical Cyclones

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